Super elastic alloy guidewire

ABSTRACT

This invention is a surgical device. It is a guidewire for use in a catheter and is used for accessing a targeted site in a lumen system of a patient&#39;s body. The guidewire may be of a high elasticity metal alloy, preferably a Ni-Ti alloy, having specified physical parameters, and is especially useful for accessing peripheral or soft tissue targets. A special variation of the inventive guidewire includes the concept of coating the wire with a one or more lubricious polymers to enhance its suitability for use within catheters and with the interior of vascular lumen. The &#34;necked&#34; guidewire tip also forms a specific variant of the invention.

FIELD OF THE INVENTION

This invention is a surgical device. It is a guidewire for use in acatheter and is used for accessing a targeted site in a lumen system ofa patient's body. The guidewire may be of a high elasticity metal alloy,preferably a Ni-Ti alloy, having specified physical parameters, and isespecially useful for accessing peripheral or soft tissue targets. Aspecial variation of the inventive guidewire includes the coating of thewire with a one or more lubricious polymers to enhance its suitabilityfor use within catheters and with the interior of vascular lumen. The"necked" guidewire tip also forms a specific variant of the invention.

BACKGROUND OF THE INVENTION

Catheters are used increasingly as a means for delivering diagnostic andtherapeutic agents to internal sites within the human body that can beaccessed through the various of the body's lumen systems, particularlythrough the vasculature. A catheter guidewire is used for guiding thecatheter through the bends, loops, and branches forming the bloodvessels within the body. One method of using a guidewire to direct thecatheter through the torturous paths of these systems of lumen involvesthe use of a torgueable guidewire which is directed as a unit from abody access point such as the femoral artery to the tissue regioncontaining the target site. The guidewire is typically bent at itsdistal end, and may be guided by alternately rotating and advancing theguidewire along the small vessel pathway to the desired target.Typically the guidewire and the catheter are advanced by alternatelymoving the guidewire along a distance in the vessel pathway, holding theguidewire in place, and then advancing the catheter along the axis ofthe guidewire until it reaches the portion of the guidewire alreadyadvanced farther into the human body.

The difficulty in accessing remote body regions, the body's periphery orthe soft tissues within the body such as the brain and the liver, areapparent. The catheter and its attendant guidewire must be bothflexible, to allow the combination to follow the complicated paththrough the tissue, and yet stiff enough to allow the distal end of thecatheter to be manipulated by the physician from the external accesssite. It is common that the catheter is as long as a meter or more.

The catheter guidewires used in guiding a catheter through the humanvasculature have a number of variable flexibility constructions. Forinstance, U.S. Pat. Nos. 3,789,841; 4,545,390; and 4,619,274 showguidewires in which the distal end section of the wire is tapered alongits length to allow great flexibility in that remote region of theguidewire. This is so, since the distal region is where the sharpestturns are encountered. The tapered section of the wire is often enclosedin a wire coil, typically a platinum coil, to increase the columnstrength of the tapered wire section without significant loss offlexibility in that region and also to increase the radial capacity ofthe guidewire to allow fine manipulation of the guidewire through thevasculature.

Another effective guidewire design is found in U.S. Pat. No. 5,095,915which shows a guidewire having at least two sections. The distal portionis encased in an elongated polymer sleeve having axially spaced groovesto allow increased bending flexibility of the sleeve.

Others have suggested the use of guidewires made of varioussuper-elastic alloys in an attempt to achieve some of the notedfunctional desires.

U.S. Pat. No. 4,925,445, to Sakamoto et al., suggests the use of atwo-portion guidewire having a body portion relatively high in rigidityand a distal end portion which is comparatively flexible. At least oneportion of the body and the distal end portions is formed ofsuper-elastic metallic materials. Although a number of materials aresuggested, including Ni-Ti alloys of 49 to 58% (atm) nickel, the patentexpresses a strong preference for Ni-Ti alloys in which thetransformation between austentite and martensite is complete at atemperature of 10° C. or below. The reason given is that "for theguidewire to be useable in the human body, it must be in the range of10° to 20° C. due to anesthesia at a low body temperature." Thetemperature of the human body is typically about 37° C.

Another document disclosing a guidewire using a metal alloy having thesame composition as a Ni-Ti super-elastic alloy is WO91/15152 (toSahatjian et al. and owned by Boston Scientific Corp.). That disclosuresuggests a guidewire made of the precursor to the Ni-Ti elastic alloy.Super-elastic alloys of this type are typically made by drawing an-ingotof the precursor alloy while simultaneously heating it. In theunstressed state at room temperature, such super-elastic materials occurin the austenite crystalline phase and, upon application of stress,exhibit stress-induced austenite-martensite (SIM) crystallinetransformations which produce nonlinear elastic behavior. The guidewiresdescribed in that published application, on the other hand, are said notto undergo heating during the drawing process. The wires are cold-drawnand great pain is taken to assure that the alloy is maintained wellbelow 300° F. during each of the stages of its manufacture. Thistemperature control is maintained during the step of grinding theguidewire to form various of its tapered sections.

U.S. Pat. No. 4,665,906 suggests the use of stress-induced martensite(SIM) alloys as constituents in a variety of different medical devices.Such devices are said to include catheters and cannulas.

U.S. Pat. No. 4,969,890 to Sugita et al., suggests the production of acatheter having a main body fitted with a shape memory alloy member, andhaving a liquid injection means to supply a warming liquid to allow theshape memory alloy member to recover its original shape upon beingwarmed by the fluid.

U.S. Pat. No. 4,984,581, to Stice, suggests a guidewire having a core ofa shape memory alloy, the guidewire using the two-way memory propertiesof the alloy to provide both tip-deflecting and rotational movement tothe guidewire in response to a controlled thermal stimulus. Thecontrolled thermal stimulus in this instance is provided throughapplication of an RF alternating current. The alloy selected is one thathas a transition temperature between 36° C. and 45° C. The temperature36° C. is chosen because of the temperature of the human body; 45° C. ischosen because operating at higher temperatures could be destructive tobody tissue, particularly some body proteins.

U.S. Pat. No. 4,991,602 to Amplatz et al., suggests a flexible guidewiremade up of a shape memory alloy such as the nickel-titanium alloy knownas nitinol. The guidewire is one having a single diameter throughout itsmidcourse, is tapered toward each end, and has a bead or ball at each ofthose ends. The bead or ball is selected to allow ease of movementthrough the catheter into the vasculature. The guidewire is symmetricalso that a physician cannot make a wrong choice in determining which endof the guidewire to insert into the catheter. The patent suggests thatwound wire coils at the guidewire tip are undesirable. The patentfurther suggests the use of a polymeric coating (PTFE) and ananticoagulant. The patent does not suggest that any particular type ofshape memory alloy or particular chemical or physical variations ofthese alloys are in any manner advantageous.

Another catheter guidewire using Ni-Ti alloys is described in U.S. Pat.No. 5,069,226, to Yamauchi, et al. Yamauchi et al. describes a catheterguidewire using a Ni-Ti alloy which additionally contains some iron, butis typically heat-treated at a temperature of about 400° to 500° C. soas to provide an end section which exhibits pseudo-elasticity at atemperature of about 37° C. and plasticity at a temperature below about80° C. A variation is that only the end portion is plastic at thetemperatures below 80° C.

U.S. Pat. No. 5,171,383, to Sagae, et al., shows a guidewire producedfrom a super-elastic alloy which is then subjected to a heat treatmentsuch that the flexibility is sequentially increased from its proximalportion to its distal end portions. A thermoplastic coating or coilspring may be placed on the distal portion of the wire material.Generally speaking, the proximal end portion of the guidewire maintainsa comparatively high rigidity and the most distal end portion is veryflexible. The proximal end section is said in the claims to have a yieldstress of approximately five to seven kg/mm² and an intermediate portionof the guidewire is shown in the claims to have a yield stress ofapproximately 11 to 12 kg/mm².

Published European Patent Application 0,515,201-A1 also discloses aguidewire produced at least in part of a superelastic alloy. Thepublication describes a guidewire in which the most distal portion canbe bent or curved into a desired shape by a physician immediately priorto use in a surgical procedure. Proximal of the guide tip, the guidewireis of a superelastic alloy. Although nickel-titanium alloys are said tobe most desirable of the class shown in that disclosure, no particularphysical description of those alloys is disclosed to be any moredesirable than another.

Published European Patent Application 0,519,604-A2 similarly discloses aguidewire which may be produced from a superelastic material such asnitinol. The guidewire core is coated with a plastic jacket, a portionof which may be hydrophilic and a portion of which is not.

Examples of Ni-Ti alloys are disclosed in U.S. Pat. Nos. 3,174,851;3,351,463; and 3,753,700.

None of these disclosures suggest the guidewire composition orconfiguration described below.

SUMMARY OF THE INVENTION

This invention is a guidewire, preferably a guidewire suitable forintroduction into the vasculature of the brain, and a method for itsuse. At least a distal portion of the guidewire may be of asuper-elastic alloy which preferably is a Ni-Ti alloy having specificphysical characteristics, e.g., a stress-strain plateau at about 75±10ksi and another at 25±7.5 ksi (each measured at 3% strain) when thestress-strain relationship is measured to a strain of 6%.

A highly desirable variation of the inventive guidewire comprises a longwire having a proximal section, an intermediate section, and a distalsection. The guidewire further may have an eccentricity ratio of 1±10⁻⁴.The distal end section is typically the most flexible of the sectionsand is at least about three centimeters long. Desirably, the flexibledistal end section is partially tapered and is covered by a coilassembly which is connected to the distal end of the guidewire at itsdistal tip. The coil assembly may be attached to the distal tip bysoldering, perhaps after plating or coating the distal end section witha malleable or solderable metal, such as gold. The guidewire assemblymay be coated with a polymer or other material to enhance its ability totraverse the lumen of the catheter. A lubricious polymer may be placeddirectly upon the core wire or upon a "tie" layer. The tie layer may bea shrink-wrap tubing or a plasma deposition or may be a dip or spraycoating of an appropriate material. The tie layer may also be radioopaque.

The guidewire of this invention may be of a composite in which a distalportion of the core is a super-elastic alloy of the type described belowand the more proximal section or sections are of another material orconfiguration, e.g., stainless steel wire or rod, stainless steelhypotube, super-elastic alloy tubing, carbon fiber tubing, etc.

Ideally there will be one or more radiopaque markers placed upon theguidewire, e.g., at its distal tip and potentially along the length ofthe intermediate section. These markers may be used both to enhance theguidewire's radiopacity and its ability to transmit torque from theproximal end to the distal end while maintaining a desired flexibility.

A specific variation of the inventive guidewire includes a distalguidewire section having a "neck" or portion of smaller diametersurrounded by areas of larger diameter thereby allowing secure solderingof a ribbon or wire within a coil assembly which extends beyond theguidewire core distal end. The enclosed ribbon or wire may be bent orshaped prior to insertion of the guidewire into the catheter tofacilitate movement of the guidewire through turns in the vasculature.

Another physical variation of this invention involves the use of groovesin the guidewire to enhance flexibility in those sections withoutsacrificing the guidewire's columnar strength.

This invention also includes a catheter apparatus made up of theguidewire core and a thin-walled catheter designed to be advanced alongthe guidewire through the vasculature for positioning at a desired site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic side view (not to scale) of the majorcomponents of the inventive guidewire.

FIG. 2 is a partial cutaway, side view of composite guidewire accordingto this invention having distal portion of a highly elastic alloy.

FIG. 3 is a partial cutaway side view of one embodiment of the distaltip of the FIG. 1 device.

FIG. 4 is a partial cutaway side view of a second embodiment of thedistal tip of the FIG. 1 device.

FIG. 5A is a partial cutaway side view of a third embodiment of thedistal tip of the FIG. 1 device.

FIG. 5B is a partial cutaway top view of the embodiment shown in FIG.5A.

FIG. 6 is a partial side view of a midsection joint in the inventiveguidewire.

FIG. 7 shows a typical stress-strain diagram for a Ni-Ti alloydisplaying objective criteria for selection of alloys for the inventiveguidewire.

DESCRIPTION OF THE INVENTION

FIG. 1 shows an enlarged side view of a guidewire made according to avery desirable variation of the inventive guidewire (100). The guidewire(100) is made up of the wire core formed of a flexible torqueable wirefilament material, of the alloys described below, and has a total lengthtypically between about 50 and 300 centimeters. The proximal section(102) preferably has a uniform diameter (along its length) of about0.010 to 0.025 inches, preferably 0.010 to 0.018 inches. The relativelymore flexible distal section (104) extends for 3 to 30 centimeters ormore of the distal end of the guidewire (100). There may be a middlesection (106) having a diameter intermediate between the diameter of thetwo portions of the wire adjoining the middle section. The middlesection (106) may be continuously tapered, may have a number of taperedsections or sections of differing diameters, or may be of a uniformdiameter along its length. If middle section (106) is of a generallyuniform diameter, the guidewire core will neck down as is seen at (108).The distal section (104) of the guidewire (100 ) typically has an endcap (110), a fine wire coil (112), and a solder joint (114). The finewire coil (112) may be radiopaque and made from materials including butnot limited to platinum and its alloys. Specific inventive variations ofthe distal section (104) are described below. The end cap (110) may beradiopaque to allow knowledge of the position of the coil (112) duringthe process of inserting the catheter and traversal of the guidewirethrough the vasculature. All or part of the guidewire proximal section(102) and middle section (106) and distal section (104) may be coatedwith a thin layer (116) of polymeric material to improve its lubricitywithout adversely affecting the flexibility or shapeability of theguidewire.

FIG. 2 shows a variation of the inventive guidewire which is acomposite, e.g., a distal portion of the guidewire core is produced ofthe specified alloy and the composite is of another material orconfiguration. In particular, the composite guidewire (140) is made upof a proximal section (142) that is a section of small diameter tubingof, e.g., an appropriate stainless steel or high elasticity alloy suchas those discussed elsewhere herein. The tubular proximal section (142)is attached by soldering or by gluing or by other joining methodsuitable for the materials involved at the joint (144) to a distalsection (146) that extends to the distal end of the composite guidewireassembly (140). The distal tip (148) of the catheter assembly (140) maybe of the same configuration as those otherwise described herein. Thecatheter assembly may be coated (150) with polymeric material, asdesired.

FIG. 3 shows a partial cutaway of one embodiment of the distal section(104) and the distal end of the intermediate section (106). The metallicguidewire core is shown partially coated with polymer (116) and amalleable metal coating (118) on the tapered portion of the distal tip.The malleable metal may be selected from suitable radiopaque materialssuch as gold or other easily solderable materials such as silver,platinum, palladium, rhodium, and alloys of the above. The tip alsoincludes a radiopaque coil (112) which is bounded on its proximal end bya solder joint (114) and is joined with the end of the guidewire at(110). The radiopaque coil (112) may be made of known suitable materialssuch as platinum, palladium, rhodium, silver, gold, and their alloys.Preferred is an alloy containing platinum and a small amount oftungsten. The proximal and distal ends of coil (112) may be secured tothe core wire by soldering.

FIG. 4 shows a partial cutaway of another embodiment of the distalsection (104) of the inventive guidewire. In this embodiment, the metalguidewire core has a proximal tapered portion (120), a distal taperedsection (122) with a solder joint (114) separating the two sections, anda constant diameter tip (124). The distal tip (124) may have constantdiameter typically between about 0.002 and 0.005 inches, preferablyabout 0.003 inches. The distal tip (124) is preferably between about 1and 5 cm in length, preferably about 2 cm but the portion of constantdiameter extends for at least about 25% of the distance between thesolder joint (128) and the solder joint (114). This constant diametersection marginally stiffens the distal tip assembly for enhancedcontrol. The entire distal section (104) desirably is between about 20and 50 cm, preferably about 25 cm in length. The maximum diameter of theproximal tapered portion (120) of the guidewire core typically isbetween about 0.005 and 0.020 inches, preferably about 0.010 inches. Thedistal tapered portion (122) and distal tip (124) are again shown with amalleable metal coating (118) such that the distal tapered portion (122)and distal tip (124) stay bent upon forming by the physician. In thisembodiment, the fine wire coil (112) is bounded on its proximal end by asolder joint (114) and on its distal end by an end cap (110). The endcap (110) is connected to the guidewire by means of a metallic ribbon(126). The ribbon (126) may be made of stainless steel, platinum,palladium, rhodium, silver, gold, tungsten, and their alloys or othermaterials which are plastic and that are easily soldered. The ribbon(126) is soldered to the fine wire coil (112) and to the distal tip(124) of the distal section (104) of the guidewire at a solder joint(128) such that the end cap (110) is secured against the fine wire coil(112).

FIGS. 5A and 5B show yet another inventive embodiment of the distalsection (104) of the guidewire (100). FIG. 5A shows a side view, partialcutaway of the inventive guidewire. The fine wire coil (112) may bebounded by a polymer adhesive (136) that joins the coil (112) to thecore wire and an end cap (110) and further secured to the guidewire coreby a solder joint (128). In this embodiment, the distal section (104) ofthe guidewire again comprises a tapered portion (120) that is proximalto the polymer adhesive (136) and a tapered portion (122) that is distalto the polymer adhesive (136). The distal section (104) also comprises asmaller diameter portion (130) or "neck" that may be surrounded byoptional inner coil (132). As may be seen from FIG. 5A, just distal ofthe neck (130) is a section which is larger in side view than is theneck. As may be seen from FIG. 5A, just distal of the neck (130 ) is asection which is larger in side view than is the neck. The inner coil(132) may be made of a suitable metallic material preferably that iseasy to solder and preferably radiopaque. It is preferably platinum orstainless steel. One way to produce neck (130) is to flatten the distalportion of the guidewire (134) distal to the neck so that the resultingspade (134) is no longer of circular cross-section but rather is ofrectangular shape. This may be more easily visualized in FIG. 5B sincethat Figure shows a cutaway top view of the guidewire shown in FIG. 5A.As in above-described embodiments, the end cap (110) is secured to theguidewire by a metallic ribbon (126). The solder joint (128) secures theguidewire core to the inner helical coil (132) which secures the end cap(110) via the ribbon (126) and further secures the outer fine wire coil(112). This configuration is especially valuable for use with guidewirematerials which are not easily solderable. The solder joint need notadhere to the guidewire and yet the inner coil (132), ribbon (126), andouter fine wire coil (112) all are maintained as a single integral unitand have no chance of slipping proximally or distally on the guidewireassembly.

Although the embodiment described with reference to FIGS. 5A and 5Bspeaks generally of a guidewire made of a high elasticity alloy,materials for the guidewire and the ribbon such as stainless steel,platinum, palladium, rhodium and the like are suitable with thatembodiment.

FIG. 6 is a partial side view of a midsection joint in the inventiveguidewire. On many variations of the inventive guidewire, varioussections of the core are joined by tapered sections such as seen at(160). This means that the guidewire core is significantly stiffer atthe proximal end of the tapered joint (160). We have found that it issometimes desirable to place grooves (162) in that proximal end to lowerthe overall stiffness of the guidewire at that junction and yet retainthe columnar strength.

GUIDEWIRE CORE

This guidewire is typically used in a catheter which is made up of anelongate tubular member having proximal and distal ends. The catheter is(again) about 50 to 300 centimeters in length, typically between about100 and 200 centimeters in length. Often, the catheter tubular memberhas a relatively stiff proximal section which extends along a majorportion of the catheter length and one or more relatively flexibledistal sections which provide greater ability of the catheter to trackthe guidewire through sharp bends and turns encountered as the catheteris advanced through the torturous paths found in the vasculature. Theconstruction of a suitable catheter assembly having differentialflexibility along its length is described in U.S. Pat. No. 4,739,768.

We have found that certain alloys, particularly Ni-Ti alloys, retaintheir super-elastic properties during traversal through the vasculatureand yet are sufficiently pliable that they provide the physician usingthe guidewire with enhanced "feel" or feedback and yet do not "whip"during use. That is to say, as a guidewire is turned it stores energyduring as a twist and releases it precipitously as it "whips" to quicklyrecover the stored stress. The preferred alloys do not incur significantunrecovered strain during use. We have also found that if theeccentricity of the wire, i.e., the deviation of the cross-section ofthe guidewire from "roundness" (particularly in the middle section) ismaintained at a very low value, the guidewire is much easier to steer ordirect through the vasculature.

The material used in the guidewires of this invention are of shapememory alloys which exhibit super-elastic/pseudo-elastic shape recoverycharacteristics. These alloys are known. See, for instance, U.S. Pat.Nos. 3,174,851 and 3,351,463 as well as 3,753,700; however, the '700patent describes a less desirable material because of the higher modulusof the material due to an increased iron content. These metals arecharacterized by their ability to be transformed from an austeniticcrystal structure to a stress-induced martensitic (SIM) structure atcertain temperatures, and return elastically to the austenitic structurewhen the stress is removed. These alternating crystalline structuresprovide the alloy with its super-elastic properties. One such well-knownalloy, nitinol, is a nickel-titanium alloy. It is readily commerciallyavailable and undergoes the austenite-SIM-austenite transformation at avariety of temperature ranges between -20° C. and 30° C.

These alloys are especially suitable because of their capacity toelastically recover almost completely to the initial configuration oncethe stress is removed. Typically there is little plastic deformation,even at relatively high strains. This allows the guidewire to undertakesubstantial bends as it passes through the body's vasculature, and yetreturn to its original shape once the bend has been traversed withoutretaining any hint of a kink or a bend. However, the tips shown areoften sufficiently plastic that the initial tip formation is retained.Nevertheless, compared to similar stainless steel guidewires, less forceneed be exerted against the interior walls of the vessels to deform theguidewire of the invention along the desired path through the bloodvessel thereby decreasing trauma to the interior of the blood vessel andreducing friction against the coaxial catheter.

A guidewire, during its passage through the vasculature to its targetsite, may undertake numerous bends and loops. The desirably of enhancingthe ease with which a guidewire may be twisted to allow the bent distaltip to enter a desired branch of the vasculature cannot be overstated.We have found that a major factor in enhancing such ease of use, thatis, in enhancing the controllability of the guidewires is by controllingthe eccentricity of the cross-section of the middle portion of theguidewire. We have found that by maintaining the middle portion of theguidewire (106 in FIG. 1) to an eccentricity ratio of 1±10⁻⁴, theguidewire is significantly more controllable than those which falloutside this ratio. By "eccentricity", we mean that at any point alongthe guidewire the ratio of the largest diameter at that cross-section tothe smallest diameter of the wire at that cross-section.

To achieve these results of high strength and enhanced control evenwhile allowing feedback to the attending physician during use, we havefound that the following physical parameters of the alloy are important.In a stress-strain test as shown on a stress-strain diagram such as thatfound in FIG. 7, the stress found at the midpoint of the upper plateau(UP) (measured, e.g. at about 3% strain when the test end point is about6% strain) should be in the range of 75 ksi (thousand pounds per squareinch) +10 ksi and, preferably, in the range of 75 ksi±5 ksi.Additionally, this material should exhibit a lower plateau (LP) of25±7.5 ksi, preferably 20±2.5 ksi, measured at the midpoint of the lowerplateau. The material preferably has no more than about 0.25% residualstrain (RS) (when stressed to 6% strain and allowed to return) andpreferably no more than about 0.15% residual strain.

The preferred material is nominally 50.6%±0.2% Ki and the remainder Ti.The alloy should contain no more than about 500 parts per million of anyof O, C, or N. Typically such commercially available materials will besequentially mixed, cast, formed, and separately co-worked to 30-40%,annealed and stretched.

By way of further explanation, FIG. 7 shows a stylized stress-straindiagram showing the various parameters noted above and their measurementon that diagram. As stress is initially applied to a sample of thematerial, the strain is at first proportional (a) until the phase changefrom austentite to martensite begins at (b). At the upper plateau (UP),the energy introduced with the applied stress is stored during theformation of the quasi-stable martensite phase orstress-induced-martensite (SIM). Upon substantial completion of thephase change, the stress-strained relationship again approaches aproportional relationship at (c). The stress is no longer applied whenthe strain reaches 6%. The measured value (UP) is found at the midpointbetween zero and 6% strain, i.e., at 3% strain. If another terminalcondition of strain is chosen, e.g., 7%, the measured valued of (UP) and(LP) would be found at 3.5%.

Materials having high UP values produce guidewires which are quitestrong and allow exceptional torque transmission but cause a compromisein the resulting "straightness" of the guidewire. We have found thatguidewires having high UP values in conjunction with high LP values arenot straight. These guidewires are difficult to use because of theirtendency to "whip" as they are turned. Again, that is to say, as aguidewire is turned it stores energy during as a twist and releases itquickly. The difficulty of using such a whipping guidewire should beapparent. Materials having UP values as noted above are suitable asguidewires.

Furthermore, materials having values of LP which are high, again, arenot straight. Lowering the value of LP compromises the ability of theguidewire to transmit torque but improves the ease with which a straightguidewire may be produced. Lowering the LP value too far, however,results in a guidewire which, although round, has poor tactile response.It feels somewhat "vague" and "soupy" during its use. The LP valuesprovided for above allow excellent torque transmission, straightness,and the valuable tactile response.

The values of residual strain discussed above define a materials whichdo not kink or otherwise retain a "set" or configuration after stressduring use as a guidewire.

EXAMPLE

In each instance, the following procedure was used in producing the datadisplayed in the table which follows: commercial Ni-Ti alloy wireshaving a nominal composition of 50.6% Ni and the remainder Ti, anddiameters of 0.13", 0.16", or 0.18" were stressed at room temperature.In each instance, values for transition temperature, PS, UP, and LP weremeasured. Additionally, several of the noted wires were introduced intoa U-shaped Tygon tube and spun to allow qualitative evaluation of theroundness and tactile response of the wires. Comments on that responseare also found in the following table.

                  TABLE                                                           ______________________________________                                            Comparative/                                                                        Invention                                                                              UP     LP                                                                                  PS                                                                                 A*                                                                                         Qualitative                 #     (C/I)          (ksi)                                                                           (ksi)                                                                                (%)                                                                                 T ° C.                                                                     Spin Test                             ______________________________________                                        1.sup.1                                                                           I          74.48  31.45                                                                              0.06  -11   Smooth rotation,                                                               good feel                             2.sup.2                                                                                 I         76.94                                                                             18.90                                                                             0.121                                                                               -8      Smooth rotation,                                                            good feel                             3.sup.3                                                                                 I         71.92                                                                             24.06                                                                               0.10                                                                               13.5                                                                                  Smooth                             4.sup.4                                                                                 C         78.24                                                                             58.82                                                                               0.20                                                                               -9     Very rough                                                                  turning, whipped                      5.sup.5                                                                                 C         63.80                                                                             13.25                                                                               0.2                                                                                 12.5                                                                                 Smooth turning,                                                            mushy feel                            6.sup.6                                                                                 C         58.30                                                                             13.31                                                                               0.0                                                                                 -12                                                                                Turned roughly,                                                              mushy feel                            7.sup.7                                                                                 C          --                                                                               --     --                                                                                --      Difficult to                       ______________________________________                                                                               turn                                    .sup.1 Commercially available from U.S. Nitinol, Inc.                         .sup.2 Commercially available from Special Metals, Inc.                       .sup.3 Commercially available from Shape Metal Alloys, Inc.                   .sup.4 Commercially available as a plastic coated 0.13"  guidewire from       Fuji Terumo, Inc.                                                             .sup.5 Commercially available from ITI.                                       .sup.6 Commercially available from Metal Tek                                  .sup.7 Stainless Steel                                                        *Measured at room temperature with no applied stress.                    

These data describe both guidewires made according to the invention andcomparative guidewires. Additionally, they show that guidewire made froma typical stainless steel alloy is very difficult to turn using thequalitative test described above.

GUIDEWIRE CORE COATINGS

As mentioned above, all or part of the guidewire core may be covered orcoated with one or more layers of a polymeric material. The coating isapplied typically to enhance the lubricity of the guidewire core duringits traversal of the catheter lumen or the vascular walls.

Coating Materials

As noted above, at least a portion of the guidewire core may simply becoated by dipping or spraying or by similar process with such materialsas polysulfones, polyfluorocarbons (such as TEFLON), polyolefins such aspolyethylene, polypropylene, polyesters (including polyamides such asthe NYLON's), and polyurethanes; their blends and copolymers such aspolyether block amides (e.g., PEBAX).

It is often desirable to utilize a coating such as discussed just aboveon the proximal portion of the guidewire and a coating such as discussedbelow on the more distal sections. Any mixture of coatings placedvariously on the guidewire is acceptable as chosen for the task at hand.

The guidewire core may also be at least partially covered with otherhydrophilic polymers including those made from monomers such as ethyleneoxide and its higher homologs; 2-vinyl pyridine; N-vinylpyrrolidone;polyethylene glycol acrylates such as mono-alkoxy polyethylene glycolmono(meth) acrylates, including mono-methoxy triethylene glycol mono(meth) acrylate, mono-methoxy tetraethylene glycol mono (meth) acrylate,polyethylene glycol mono (meth) acrylate; other hydrophilic acrylatessuch as 2-hydroxyethylmethacrylate, glycerylmethacrylate; acrylic acidand its salts; acrylamide and acrylonitrile; acrylamidomethylpropanesulfonic acid and its salts cellulose, cellulose derivatives such asmethyl cellulose ethyl cellulose, carboxymethyl cellulose, cyanoethylcellulose, cellulose acetate, polysaccharides such as amylose, pectin,amylopectin, alginic acid, and cross-linked heparin; maleic anhydride;aldehydes. These monomers may be formed into homopolymers or block orrandom copolymers. The use of oligomers of these monomers in coating theguidewire for further polymerization is also an alternative. Preferredprecursors include ethylene oxide; 2-vinyl pyridine; N-vinylpyrrolidoneand acrylic acid and its salts; acrylamide and acrylonitrile polymerized(with or without substantial crosslinking) into homopolymers, or intorandom or block copolymers.

Additionally, hydrophobic monomers may be included in the coatingpolymeric material in an amount up to about 30% by weight of theresulting copolymer so long as the hydrophilic nature of the resultingcopolymer is not substantially compromised. Suitable monomers includeethylene, propylene, styrene, styrene derivatives, alkylmethacrylates,vinylchloride, vinylidenechloride, methacrylonitrile, and vinyl acetate.Preferred are ethylene, propylene, styrene, and styrene derivatives.

The polymeric coating may be cross-linked using various techniques,e.g., by light such as ultraviolet light, heat, or ionizing radiation,or by peroxides or azo compounds-such as acetyl peroxide, cumylperoxide, propionyl peroxide, benzoyl peroxide, or the like. Apolyfunctional monomer such as divinylbenzene, ethylene glycoldimethacrylate, trimethylolpropane, pentaerythritol di- (or tri- ortetra-) methacrylate, diethylene glycol, or polyethylene glycoldimethacrylate, and similar multifunctional monomers capable of linkingthe monomers and polymers discussed above.

Polymers or oligomers applied using the procedure described below areactivated or functionalized with photoactive or radiation-active groupsto permit reaction of the polymers or oligomers with the underlyingpolymeric surface. Suitable activation groups include benzophenone,thioxanthone, and the like; acetophenone and its derivatives specifiedas:

    Ph

    C═O

    R.sup.1 --C--R.sup.3

    R.sup.2

where

R¹ is H, R² is OH, R³ is Ph; or

R¹ is H, R² is an alkoxy group including--OCH₃, --OC₂ H₃, R³ is Ph; or

R¹ =R² =an alkoxy group, R³ is Ph; or

R¹ =R² =an alkoxy group, R³ is H; or

R¹ =R² =Cl, R³ is H or Cl.

Other known activators are suitable.

The polymeric coating may then be linked 25 with the substrate usingknown and appropriate techniques selected on the basis of the chosenactivators, e.g., by ultraviolet light, heat, or ionizing radiation.Crosslinking with the listed polymers or oligomers may be accomplishedby use of peroxides or azo compounds such as acetyl peroxide, cumylperoxide, propionyl peroxide, benzoyl peroxide, or the like. Apolyfunctional monomer such as divinylbenzene, ethylene glycoldimethacrylate, trimethylolpropane, pentaerythritol di- (or tri- ortetra-) methacrylate, diethylene glycol, or polyethylene glycoldimethacrylate, and similar multifunctional monomers capable of linkingthe polymers and oligomers discussed above is also appropriate for thisinvention.

The polymeric coating may be applied to the guidewire by any of avariety of methods, e.g., by spraying a solution or suspension of thepolymers or of oligomers of the monomers onto the guidewire core or bydipping it into the solution or suspension. Initiators may be includedin the solution or applied in a separate step. The guidewire may besequentially or simultaneously dried to remove solvent after applicationof the polymer or oligomer to the guidewire and crosslinked.

The solution or suspension should be very dilute since only a very thinlayer of polymer is to be applied. We have found that an amount ofoligomer or polymer in a solvent of between 0.25% and 5.0% (wt),preferred is 0.5 to 2.0% (wt), is excellent for thin and completecoverage of the resulting polymer. Preferred solvents for this procedurewhen using the preferred polymers and procedure are water, low molecularweight alcohols, and ethers, especially methanol, propanol, isopropanol,ethanol, and their mixtures. Other water miscible solvents, e.g.,tetrahydrofuran, methylene dichloride, methylethylketone,dimethylacetate, ethyl acetate, etc., are suitable for the listedpolymers and must be chosen according to the characteristics of thepolymer; they should be polar because of the hydrophilic nature of thepolymers and oligomers but, because of the reactivity of the terminalgroups of those materials, known quenching effects caused by oxygen,hydroxyl groups and the like must be recognized by the user of thisprocess when choosing polymers and solvent systems.

Particularly preferred as a coating for the guidewire cores discussedherein are physical mixtures of homo-oligomers of at least one ofpolyethylene oxide; poly-2-vinyl pyridine; polyvinylpyrrolidone,polyacrylic acid, polyacrylamide, and polyacrylonitrile. The catheterbodies or substrates are preferably sprayed or dipped, dried, andirradiated to produce a polymerized and crosslinked polymeric skin ofthe noted oligomers.

The lubricious hydrophilic coating is preferably produced usinggenerally simultaneous solvent removal and crosslinking operations. Thecoating is applied at a rate allowing "sheeting" of the solution, e.g.,formation of a visibly smooth layer without "runs". In a dippingoperation for use with most polymeric substrates including those notedbelow, the optimum coating rates are found at a linear removal ratebetween 0.25 and 2.0 inches/sec, preferably 0.5 and 1.0 inches/sec.

The solvent evaporation operations may be conducted using a heatingchamber suitable for maintaining the surface at a temperature between25° C. and the glass transition temperature (T_(g)) of the underlyingsubstrate. Preferred temperatures are 50° C. to 125° C. Most preferredfor the noted and preferred solvent systems is the range of 75° to 110°C.

Ultraviolet light sources may be used to crosslink the polymerprecursors onto the substrate. Movement through an irradiation chamberhaving an ultraviolet light source at 90-375 nm (preferably 300-350 nm)having an irradiation density of 50-300 mW/cm² (preferably 150-250mW/cm²) for a period of three to seven seconds is desired. Passage of aguidewire core through the chamber at a rate of 0.25 to 2.0inches/second (0.5 to 1.0 inches/second) in a chamber having three tonine inches length is suitable. When using ionizing radiation, aradiation density of 1 to 100 kRads/cm² (preferably 20 to 50 kRads/cm²)may be applied to the solution or suspension on the polymeric substrate.

Exceptional durability of the resulting coating is produced byrepetition of the dipping/solvent removal/irradiation steps up to fivetimes. Preferred are two to four repetitions.

Tie Layers

We have found that it is often desirable to incorporate a "tie" layer asa coating between the outer polymeric surface and the guidewire core toenhance the overall adhesion of the outer polymeric surface to the core.Of course, these materials must be able to tolerate the various othersolvents, cleaners, sterilization procedures, etc. to which theguidewire and its components are placed during other production steps.

Choice of materials for such tie layers is determined through theirfunctionality. Specifically, the materials are chosen for their affinityor tenacity to the outer polymeric lubricious or hydrophilic coating.Clearly, the tie layer material must be flexible and strong. Thematerial must be extrudable and preferably easily made into shrinkabletubing for mounting onto the guidewire through heating. We have foundthat various NYLON's, polyethylene, polystyrene, polyurethane, andpreferably polyethylene terephthalate (PET) make excellent tie layers.These tubing materials may be also formulated to include radio opaquematerials such as barium sulfate, bismuth trioxide, bismuth carbonate,tungsten, tantalum or the like.

As noted above, one readily achievable manner of applying a tie layer isby heat-shrinking the tubing onto the guidewire. The guidewire core issimply inserted into a tubing of suitable size--often with a smallamount of a "caulking" it either end to seal the tubing from incursionof fluids or unsterile materials from beneath the tubing. The tubing iscut to length and heated until it is sufficiently small in size. Theresulting tubing tie layer desirably is between about 0.0025 and 0.015inches in thickness. The thinner layers are typically produced frompolyurethane or PET. The layer of lubricious polymer is then placed onthe outer surface of the shrunk tubing.

Another procedure for preparing or pretreating guidewires prior toreceiving a subsequent coating of a polymer, preferably a polymer whichis lubricious, biocompatible, and hydrophilic, is via the use of aplasma stream to deposit a hydrocarbon or fluorocarbon residue. Theprocedure is described as follows: the guidewire core is placed in aplasma chamber and cleaned with an oxygen plasma etch. The guidewirecore is then exposed to a hydrocarbon plasma to deposit aplasma-polymerized tie layer on the guidewire core to complete thepretreatment. The hydrocarbon plasma may comprise a lower molecularweight (or gaseous) alkanes such as methane, ethane, propane, isobutane,butane or the like; lower molecular weight alkenes such as ethene,propene, isobutene, butene or the like or; gaseous fluorocarbons such astetrafluoromethane, trichlorofluoromethane, dichlorodifluoromethane,trifluorochloromethane, tetrafluoroethylene, trichlorofluoroethylene,dichlorodifluoroethylene, trifluorochloroethylene and other suchmaterials. Mixtures of these materials are also acceptable. The tielayer apparently provides C--C bonds for subsequent covalent bonding tothe outer hydrophilic polymer coating. Preferred flow rates for thehydrocarbon into the plasma chamber are in the range of 500 c.c./min. to2000 c.c./min. and the residence-time of the guidewire in the chamber isin the range of 1-20 minutes, depending on the chosen hydrocarbon andthe plasma chamber operating parameters. Power settings for the plasmachamber are preferably in the range of 200 W to 1500 W.

A tie layer of plasma-produced hydrocarbon residue having a thickness onthe order of 10 Å thick is disposed between core and coating. Thisprocess typically produces layers of hydrocarbon residue less than about100 Å in thickness, and more typically less than about 100Å. Tie layereffectively bonds the outer layer to the guidewire core while addingvery little additional bulk to the guidewire. Guidewires made accordingto this invention therefore avoid the size and maneuverability problemsof prior art guidewires.

The pretreated guidewire may be coated by a polymer using a proceduresuch as described above. For example, the pretreated guidewire may bedipped in a solution of a photoactive hydrophilic polymer system, i.e.,a latently photoreactive binder group covalently bonded to a hydrophilicpolymer. After drying, the coated guidewire is cured by exposing it toUV light. The UV light activates the latently reactive group in thephotoactive polymer system to form covalent bonds with crosslinked C--Cbonds in the hydrocarbon residue tie layer. The dipping and curing stepsare preferably repeated often enough, typically twice, to achieve theappropriate thickness of the hydrophilic coating layer.

One highly preferred variation of the invention involves a guidewirewith metal core, preferably 0.010 to 0.025" thick stainless steel ornitinol. The exterior surface of guidewire is a biocompatible coating ofa polyacrylamide/polyvinylpyrrolidone mixture bonded to a photoactivebinding agent. The preferred coating is made from a mixture ofBio-Metric Systems PA03 and PV05 (or PV01) binding systems according tothe Examples below.

The photoactive hydrophilic polymer system of this preferred embodimentis a mixture of Bio-Metric Systems PA03 polyacrylamide/binder system andBio-Metric Systems PV05 polyvinylpyrrolidone system. The polyacrylamidesystem provides lubricity, and the polyvinylpyrrolidone system providesboth lubricity and binding for durability. The exact proportions of thetwo systems may be varied to suit the application. As an alternative,however, the hydrophilic biocompatible coating may be polyacrylamidealone, polyvinylpyrrolidone alone, polyethylene oxide, or any suitablecoating known in the art. In addition, a coating of heparin, albumin orother proteins may deposited over the hydrophilic coating in a mannerknown in the art to provide additional biocompatibility features.

The guidewire or other device may be cleaned by using an argon plasmaetch in place of the oxygen plasma etch. The thickness of theplasma-polymerized tie layer may also vary without departing from thescope of this invention.

The following examples are further illustrative of the articles andmethods of this invention. The invention is not limited to theseexamples.

EXAMPLE

A 0.016" diameter nitinol guidewire was placed in a Plasma Etch MK IIplasma chamber and cleaned with an oxygen plasma for 10 minutes. Methaneflowing at a rate of 2000 c.c./min. was admitted into the chamber, andthe chamber operated at a power setting of 400 W for 2 minutes todeposit a hydrocarbonaceous residue onto the surface of the wire. Allbut approximately six inches of the wire was dipped in apolyvinylpyrrolidone/polyacrylamide (PVP/PA) photocrosslinkable solutionof a mixture of 67% BSI PV01 and 33% BSI PA03. The coated guidewire wasthen dried and exposed to an ultraviolet light (325 nm.) for 8 seconds.The dipping, drying, and exposing steps were repeated twice. Whenwetted, the resulting wire felt lubricious and required less force topull through an 0.018" ID catheter than an uncoated wire.

EXAMPLE

A 0.016" diameter nitinol guidewire was placed in a Plasma Etch MK IIplasma chamber and cleaned with an oxygen plasma for 10 minutes. Methaneflowing at a rate of 1500 c.c./min. was admitted into the chamber, andthe chamber was operated at a power setting of 600 W for 5 minutes toplasma-treat the methane into a hydrocarbonaceous residue on the surfaceof the wire. All but approximately six inches of the wire was dipped ina polyvinylpyrrolidone/polyacrylamide (PVP/PA) photocrosslinkablesolution consisting essentially a mixture of 50% BSI PV01 and 50% BSIPA03. The coated guidewire was then dried and exposed to an ultravioletlight (325 nm.) for 8 seconds. The dipping, drying, and exposing stepswere repeated. When wetted, the resulting wire felt lubricious andrequired less force to pull through an 0.018" ID catheter than anuncoated wire.

EXAMPLE

A 0.016" diameter nitinol guidewire was placed in a Plasma Etch MK IIplasma chamber and cleaned with an oxygen plasma for 10 minutes. Ethaneflowing at a rate of 900 c.c./min. was admitted into the chamber, andthe chamber was operated at a power setting of 600 W for 10 minutes todeposit a hydrocarbon residue onto the surface of the wire. All butapproximately six inches of the wire was dipped in apolyvinylpyrrolidone/polyacrylamide (PVP/PA) photocrosslinkable solutionof a mixture of 33% BSI PV01 and 67% BSI PA03. The coated guidewire wasthen dried and exposed to an ultraviolet light (325 nm.) for 8 seconds.The dipping, drying, and exposing steps were repeated twice. Whenwetted, the resulting wire felt lubricious and required less force topull through an 0.01811 ID catheter than an uncoated wire.

Although preferred embodiments of the present invention have beendescribed, it should be understood that various changes, adaptations,and modifications may be made therein without departing from the spiritof the invention and the scope of the claims which follow.

I claim as my invention:
 1. A guidewire suitable for guiding a catheterwithin a body lumen, comprising an elongated, flexible metal wire coreof a super-elastic alloy having a UP of 75 ksi±10 ksi, an LP of 25ksi±7.5 ksi measured at 3% strain and a RS of less than 0.25% wheremeasured in a stress-strain test to 6% strain, in which at least aportion of the guidewire is coated with a polymeric material andadditionally comprising a tie layer disposed between the polymeric layerand the guidewire core.
 2. The guidewire of claim 1, where the guidewirehas a eccentricity ratio of 1±10⁻⁴.
 3. The guidewire of claim 1, havinga distal section, a middle section, and a proximal section.
 4. Theguidewire of claim 1, in which the super-elastic alloy is Ni-Ti.
 5. Theguidewire of claim 3, in which the distal section is tapered to a point.6. The guidewire of claim 5, in which the distal section is coated witha malleable metal.
 7. The guidewire of claim 6, in which the malleablemetal is selected from the group consisting of gold, nickel, silver,platinum, palladium and alloys thereof.
 8. The guidewire of claim 6, inwhich the at least a portion of the malleable metal coating on thedistal portion is covered by an outer coil comprising platinum,tungsten, or an alloy thereof.
 9. The guidewire of claim 4, in which thedistal section comprises a proximal tapered portion and a constantdiameter distal portion.
 10. The guidewire of claim 9, in which thedistal section is coated with a malleable metal.
 11. The guidewire ofclaim 10, in which the malleable metal is selected from the groupconsisting of gold, silver, platinum, palladium and alloys thereof. 12.The guidewire of claim 11, in which the at least a portion of themalleable metal coating on the distal portion is covered by an outercoil comprising platinum, tungsten, or an alloy thereof.
 13. Theguidewire of claim 11, wherein an inner coil surrounds the constantdiameter distal portion.
 14. The guidewire of claim 13, wherein theinner coil comprises a radiopaque metal selected from the groupconsisting of platinum, tungsten, or an alloy of the two.
 15. Theguidewire of claim 14, wherein a metallic ribbon secures the wire coreto the inner coil and further to the outer coil.
 16. The guidewire ofclaim 4, in which the distal section comprises a necked down portion ofsmaller diameter than its surrounding distal section.
 17. The guidewireof claim 16, in which at least a portion of the necked down section ofthe distal portion is covered by an outer coil.
 18. The guidewire ofclaim 4, in which the outer coil is connected at its distal end by aribbon joined to the necked down section of the distal portion.
 19. Theguidewire of claim 18, in where an inner coil is secured between theribbon and the necked down section all within the outer coil.
 20. Theguidewire of claim 1 where the polymeric material comprises polymersproduced from monomers selected from ethylene oxide; 2-vinyl pyridine;N-vinylpyrrolidone; polyethylene glycol acrylates such as mono-alkoxypolyethylene glycol mono(meth) acrylates, including mono-methoxytriethylene glycol mono (meth) acrylate, mono-methoxy tetraethyleneglycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate;other hydrophilic acrylates such as 2-hydroxyethylmethacrylate,glycerylmethacrylate; acrylic acid and its salts; acrylamide andacrylonitrile; acrylamidomethylpropane sulfonic acid and its salts,cellulose, cellulose derivatives such as methyl cellulose ethylcellulose, carboxymethyl cellulose, cyanoethyl cellulose, celluloseacetate, polysaccharides such as amylose, pectin, amylopectin, alginicacid, and cross-linked heparin.
 21. The guidewire of claim 1, where thetie layer disposed between the polymeric layer and the guidewire core isa heat shrunk tubing.
 22. The guidewire of claim 21, where the tie layerdisposed between the polymeric layer and the guidewire core is a heatshrunk tubing comprising a material selected from polyethyleneterephthalate and polyurethane.
 23. The guidewire of claim 21, where thetie layer disposed between the polymeric layer and the guidewire core isa heat shrunk tubing and further comprises a radiopaque material. 24.The guidewire of claim 1, where the tie layer disposed between thepolymeric layer and the guidewire core is deposited by plasma.
 25. Theguidewire of claim 1 additionally comprising a catheter sheath.
 26. Aguidewire suitable for guiding a catheter within a blood vessel,comprising an elongated flexible metal wire core having a distal sectionincluding a necked down portion having a diameter smaller than alinearly contiguous section just distal of the necked down portion; anouter coil surrounding at least a portion of the distal section, suchportion of the distal section comprising at least the smaller diameterportion; and a metallic ribbon securing the outer coil to the smallerdiameter portion of the distal section.
 27. The guidewire of claim 26,wherein an inner coil is located within the smaller diameter portion ofthe distal section.
 28. The guidewire of claim 26, wherein the wire corecomprises a material selected from the group consisting of highelasticity alloys, stainless steel, platinum, palladium, rhodium andalloys thereof.
 29. The guidewire of claim 28, where the material is aNi-Ti alloy.
 30. The guidewire of claim 26, wherein the outer coilcomprises a radiopaque material selected from the group consisting ofplatinum, tungsten, or an alloy of the two.
 31. The guidewire of claim26, wherein the inner coil comprises a radiopaque material selected fromthe group consisting of platinum, tungsten or an alloy of the two.
 32. Aguidewire suitable for guiding a catheter within a blood vessel,comprising an elongated flexible metal wire core of a super-elasticalloy having a tie layer disposed about at least a portion of the core,where said tie layer has been shrunk onto the wire core, where said tielayer comprises at least one of NYLON, polyethylene, polystyrene,polyurethane and polyethylene terephthalate, and where said tie layerfurther comprises one or more radio opaque material selected from bariumsulfate, bismuth trioxide, bismuth carbonate, tungsten and tantalum. 33.The guidewire of claim 32, where the super-elastic alloy material is aNi-Ti alloy.
 34. The guidewire of claim 33, where the tie layercomprises at least one of NYLON, polyethylene, polystyrene,polyurethane, and polyethylene terephthalate.
 35. The guidewire of claim34, where the tie layer comprises polyethylene terephthalate orpolyurethane.
 36. The guidewire of claim 34, where the tie layer furthercomprises one or more radio opaque materials selected from bariumsulfate, bismuth trioxide, bismuth carbonate, tungsten, and tantalum.37. The guidewire of claim 32, additionally comprising a layer disposedabout the tie layer comprising polymers produced from monomers selectedfrom ethylene oxide; 2-vinyl pyridine; N-vinylpyrrolidone; polyethyleneglycol acrylates such as mono-alkoxy polyethylene glycol mono(meth)acrylates, including mono-methoxy triethylene glycol mono (meth)acrylate, mono-methoxy tetraethylene glycol mono (meth) acrylate,polyethylene glycol mono (meth) acrylate; other hydrophilic acrylatessuch as 2-hydroxyethylmethacrylate, glycerylmethacrylate; acrylic acidand its salts; acrylamide and acrylonitrile; acrylamidomethylpropanesulfonic acid and its salts, cellulose, cellulose derivatives such asmethyl cellulose ethyl cellulose, carboxymethyl cellulose, cyanoethylcellulose, cellulose acetate, polysaccharides such as amylose, pectin,amylopectin, alginic acid, and cross-linked heparin.
 38. The guidewireof claim 26, wherein said section just distal of the necked down portionis substantially flattened and has a width greater than said diameter ofsaid necked down portion.
 39. The guidewire of claim 32, where said tielayer comprises polyethylene terephthalate or polyurethane.
 40. Aguidewire suitable for guiding a catheter within a blood vessel,comprising an elongated flexible metal wire core of a super-elasticalloy having a tie layer disposed about at least a portion of the core,where said tie layer has been shrunk onto the wire core, and a layerdisposed about said tie layer, said layer disposed about said tie layercomprising polymers produced from monomers selected from ethylene oxide;2-vinyl pyridine; N-vinylpyrrolidone; polyethylene glycol acrylates suchas mon-alkoxy polyethylene glycol mono(meth) acrylates, includingmono-methoxy triethylene glycol mono(meth) acrylate, mono-methoxytetraethylene glyco mono(meth) acrylate, polyethylene glycol mono(meth)acrylate; other hydrophilic acrylates such as2-hydroxyethylmethacrylate, glycerylmethacrylate; acrylic acid and itssalts; acrylamide and acrylonitrile; acrylamidomethylpropane sulfonicacid and its salts; cellulose; cellulose derivatives such as methylcellulose, ethyl cellulose, carboxymethyl cellulose, cyanoethylcellulose, cellulose acetate; polysaccharides such as amylose, pectin,amylopectin, alginic acid, and cross-linked heparin.
 41. The guidewireof claim 32, where the super-elastic alloy material is a Ni-Ti alloy.